In circuit arrangements, in particular electronic ballasts for operating discharge lamps which are not constructed as a freely oscillating oscillator and therefore contain component parts for controlling the electronic ballast, it is necessary to make available sufficient supply power, which is appropriate for the operating state, for these control component parts.
In general, there are two different operating states: firstly the run up state which is run through once the supply voltage has been applied and secondly the normal operating mode which occurs during operation.
The run up state is characterized by the fact that a supply capacitor is charged in a simple manner via a run up resistor which has as high a resistance value as possible, said supply capacitor at the same time acting as a buffer for the supply of at least one control component part. If the charge voltage reaches a value which is sufficient for the control component part, said control component part begins to operate and controls, for example, the transistors of the ballast; the normal operating mode has been reached. In this run up state, control component parts require significantly less current, the so-called run up current, than in the normal operating mode.
In the normal operating mode, the buffer capacitor is generally charged via a charge pump in order to make available the markedly higher current requirement of the control component parts in the normal operating mode. This charge pump generally includes two diodes and a capacitor, which is coupled firstly to a potential with a high AC voltage content, for example the half-bridge center point of a bridge circuit in the form of a half bridge, and secondly to the two diodes.
In relatively complex ballasts, there is a large number of control component parts which need to be supplied with power in the normal operating mode, but the current supply to said control component parts needs to be interrupted during the run up state in order to keep the current required for charging the supply capacitor as small as possible and therefore to minimize the losses in the run up resistor during operation.
In specific cases, it may now be necessary to cease the operation of the ballast, but nevertheless to supply current to at least individual parts of the control circuit. This may be the case, for example, if the operation of the ballast needs to be ceased owing to an excessively low supply voltage and the device needs to be set to sleep mode, but needs to be started again when there is sufficient voltage again. Other possible criteria would be, for example, a switch-off operation brought about by an operator or by an automatic timer. The determination of a value which is again sufficient for the supply voltage or renewed startup as desired by an operator or an automatic timer need to take place by means of a control component part, such as a microcontroller, for example, which needs to be supplied with a low current even in this sleep mode for this purpose.